1. Field of the Invention
The present invention relates to gas sampling systems generally and particularly to closed loop gas sampling systems which return the sample to the area from which the sample was taken.
1. Description of the Prior Art
The control of various processes such as steel making as well as combustion control systems is dependent upon an accurate monitoring and analyzing of process gases such as combustion flue gases. These gases are normally analyzed for concentrations of various elements such as oxygen, carbon monoxide, carbon dioxide, sulfur dioxide, and other combustibles. Usually, individual analyzers are provided to measure the oxygen concentration as well as the combustibles concentration in the process gases.
The mentioned individual sampling systems usually had their own indicators for providing an indication of a plugged sample inlet line. Plugging occurs due to the dirty environment of the flue and such plugging must be taken into consideration to insure the continuous accurate operation of the analyzing system. The usual type of such flow indicator has been a pressure switch operating on negative pressure that is tied into the sampling system. Thus, as the inlet line is plugged up to a predetermined amount, negative pressure increases in the system eventually causing the switch to close a contact and indicate the malfunction.
The use of the aforementioned individual sampling systems for oxygen and combustibles resulted in a great duplication of parts and required more mounting space and installation time to be adapted to the duct. What was needed was a single sampling system which would check for both oxygen and combustibles level as well as providing a single indication of proper flow through the sample line.